It is known to replenish the processing solutions used in photographic processing apparatus for processing photographic materials to maintain the solution activity and hence the results obtained.
It is also known to treat the processing solutions to recover silver and silver compounds therefrom. Examples of silver recovery techniques are described in CA 2 033 788, U.S. Pat. No. 4,445,935 and U.S. Pat. No. 5,288,728.
In CA 2 033 788, a process is described in which silver sulfide is recovered from a spent photographic fixer solution containing silver. A hydrosulfide reagent is introduced into the fixer solution to react with the silver in the solution so that it precipitates out as silver sulfide whilst maintaining the pH and thiosulfate levels in the fixer solution allowing it to be re-used.
U.S. Pat. No. 4,445,935 describes a method in which an alkaline hypochlorite solution is used to react with spent photographic fixer solution. Under these oxidizing conditions, the silver ion complexing agents of thiosulfate and sulfite ions are effectively destroyed. Hydrazine monohydrate is then added to the oxidizing solution to form a reducing solution to effect the formation of a precipitate of silver which is removed by filtration or decanting. The treated fixer solution can then be discharged to drain.
U.S. Pat. No. 5,288,728 describes a method of recovering silver from a mixture of seasoned photographic processing solutions, for example, seasoned stabilizer solution, bleach, bleach-fix and developer solutions, by contacting the mixture of solutions with a mercapto-s-triazine or water soluble salt thereof. The silver ion complexes with the mercapto-s-triazine compound and is allowed to settle out prior to being separated from the solutions.
EP 0 514 868 also discloses a method for processing a silver halide photographic light-sensitive material and recycling the processing solution used in the process. A silver compound is precipitated out of the processing solution using a precipitant and then removed to regenerate the processing solution for recycling.
In all of the methods described above, silver is recovered from the processing solution. However, this recovery tends to be carried out as a batch process. There is no automatic treatment of the effluent from the photographic process so that the treated processing solutions can be passed directly to drain.
Moreover, there is no disclosure of photographic processing apparatus in which the treatment of used processing solutions can be automatically carried out in conjunction with replenishment of the process.